Exemplary embodiments of the present invention generally relate to a driver for a light emitting diode (LED), and, more specifically, to a current sharing technology for multiple outputs of LEDs in paralleled.
For constant current control technology for multiple outputs, there are several traditional prior art techniques/methods which are used frequently. As illustrated in FIG. 1, a constant voltage circuit with multiple non-isolated DC/DC constant current circuit (e.g., Buck circuit) is disclosed, while another approach, as illustrated in FIG. 2, involves a voltage regulated circuit with adjustable output voltage connected with multiple linear regulation constant current circuit.
As further illustrated in FIG. 1, an output voltage of a constant voltage circuit 10 is an input for a constant current circuit 12 with multiple outputs. Each constant current circuit 12 is independently controlled, making it relatively easy to guarantee the current sharing for multiple outputs. A key disadvantage of such a circuit is that it is a complex circuit causing the cost to build such a circuit to be rather expensive because each constant current circuit 12 requires an independent a DC/DC converter.
As further illustrated in FIG. 2, a multiple linear regulation constant current control circuit is disclosed. Though not illustrated, each linear regulation constant current control circuit 14 comprises a MOSFET and transistors. An output voltage of a voltage regulated circuit 16 of a first stage is adaptively changed with an output of the linear regulator of a post stage. An output voltage of the first stage is always higher than a maximum output voltage of the multiple linear regulated constant current circuits, resulting in minimum power loss. An advantage of this prior art circuit is the low cost and the good current sharing capability for multiple outputs. However, a disadvantage is that the voltage controlled circuit of the first stage is not standard, but it is custom-built where the design cost is high. To ensure proper safety features are included, additional higher cost are further realized because the first stage circuit is not a standard circuit.